Active Magnetic Regenerator Research Articles

Scaling up magnetocaloric heat pump for building decarbonization initiatives

Building decarbonization necessitates renewable heating and cooling solutions such as heat pumps. Magnetocaloric heat pumps (MCHP) offer environmental and efficiency advantages but face challenges when scaling up from existing active magnetic regenerator configurations. This study highlights uneven flow resistance, porosity, and refrigerant magnetocaloric effects as key obstacles to MCHP performance in parallel multi-bed setups. To address these effects, two control strategies for the fluid flow control system were investigated: measurement feedback control and model predictive control. Results show a 36.9 % heating power improvement with measurement feedback control, though with extended control convergence times. Model predictive control achieved approximately seven times faster control convergence compared to the measurement feedback control strategy, despite exhibiting minor overshooting. Utilization factor-based model predictive control increased the heating capacity by 1.6 %–30.9 % and the COP by 1.2 %–10.7 % in scenarios with uneven flow resistance and porosity, offering computational efficiency but assuming even magnetocaloric effects between regenerators. This assumption can be addressed by outlet temperature-based model predictive control, albeit at a higher computational cost using genetic algorithm. The findings emphasize the importance of advanced control methods to scaling up MCHP in renewable energy building systems.

Experimental assessment of a multilayered packed-sphere La–Fe–Si active magnetic regenerator

This study investigates the performance of a multilayered packed-bed active magnetic regenerator (AMR) using spheroidal particles with first-order magnetocaloric properties. The hydraulic performance is assessed via the interstitial friction factor, showing significant underestimation by the Ergun Equation at high mass flow rates. Coefficient adjustments are made to accurately represent the AMR pressure drop, considering particle nonuniformity and structural components, such as layer mesh dividers. This facilitates the pressure drop modeling and provides a means to check the AMR integrity on a routine basis, without requiring AMR disassembly. The thermal performance, evaluated in terms of the regenerator effectiveness, shows a satisfactory cooling potential for practical applications but emphasizes the need for flow control to prevent effectiveness imbalance between hot and cold flows, crucial for optimal operation. The cooling capacity and maximum temperature span are also evaluated, demonstrating that higher mass flow rates yield higher cooling capacities with lower temperature spans, while lower rates achieve higher spans. Varying the blow fraction shows that regenerators at 50% blow fraction achieve 10% higher cooling capacities than at 37.5%. Increasing operational frequency improves cooling by increasing the number of cycles and reducing losses, resulting in a 15% capacity increase between 0.25 and 0.50 Hz. However, this trend may reverse at higher frequencies beyond the experimental limits. While this study improves the understanding of the hydraulic and thermal performance of packed-bed AMRs, its findings underscore the importance of flow balance and frequency in achieving optimal performance, thus providing insights for future system improvements.

Simulation of an operation of nested Halbach cylinder arrays in regenerative magnetic cooling cycles: The way to maximum thermal span

In this study, a numerical model of the Active Magnetic Regenerator (AMR) cycle, implemented in the reciprocal demonstrator, was developed using COMSOL Multiphysics. A nested Halbach cylinder (NHC) array served as the magnetic field source. Additional simulation of an operation of the NHC array was carried out. To eliminate the discrepancies between the heat exchange duration of the heat transfer medium (HTM) and the hot and cold ends of the regenerator, an adequate time dependence of the inner cylinder rotation angle was calculated. The latter provides the symmetrical sinusoidal form of time dependence of the magnetic flux density in the gap of NHC array, which is important for enhancing the performance of a magnetic refrigerator. It was established that in order to achieve a maximal temperature span, it is necessary to shift the phases of the magnetic field insertion/removal and heat transfer fluid pumping processes by nearly half of the operating cycle period. The latter brings the simulated cycle closer to the ideal AMR cycle.

Impact of magnetic, atomic and microstructural ordering on the magnetocaloric performance of powdered NiCoMnSn metamagnetic shape memory ribbons

Co-doped NiMnSn Heusler-type metamagnetic shape memory alloys (MMSMAs) are promising materials for the next-generation solid-state refrigeration systems due to their excellent magnetocaloric performance around the martensitic transformation, which is easily tuneable by slight changes in the alloy composition. An improvement in the thermal efficiency of active magnetic regenerator devices, a key element in magnetocaloric cooling systems, arises by obtaining powdered magnetocaloric alloys that meet technical requirements for their implementation as a feedstock material in the additive manufacturing of 3D-printed heat exchangers. In the present work, powders of Mn-rich NiCoMnSn Heusler-type MMSMAs were obtained from their ribbon form avoiding or minimizing residual stresses, the number of defects and disorder in the crystal lattice and microstructure. Since atomic order and crystallographic structure are crucial in the transformation and magnetic properties of these alloys, a complementary structural analysis of the powders after different heat treatments was performed by powder neutron diffraction. The results show that the cubic austenitic phase of the non-heat-treated melt-spun powder exhibits a highly stressed structure, which leads to an incomplete martensitic transformation and, therefore, to the coexistence of martensitic and austenitic phases at low temperatures. The magnetic structure of the austenite phase was also determined by neutron powder diffraction, obtaining a ferromagnetic coupling between 4a and 4b Wyckoff positions in the samples analysed. It was found that a heat treatment facilitates the martensitic transformation and enables the formation of a pure martensitic phase.The observed changes in the magnetocaloric performance of the powders have been understood in terms of the differently stressed structures and their impact on the martensitic transformation. A fully completed structural transformation leads to a significant increase of the magnetisation change across the martensitic transformation and, consequently, to high values of both a magnetic field induced isothermal entropy change and refrigeration capacity.

Performance analysis of an Active Magnetic Regenerative system using Al2O3 nanofluids

This study investigates the utilization of Al2O3 nanofluids in an Active Magnetic Regenerative (AMR) system, focusing on varying nanoparticle concentrations from 0.01 to 1.0%. Numerical modelling is used to analyze the effects of nanoparticle incorporation on system efficiency and cooling performance. Al2O3 nanoparticles are found to significantly increase the thermal conductivity, density, and viscosity of the base fluid while reducing specific heat capacity. Comparative analysis reveals that Al2O3 nanofluids outperform pure water in terms of cooling performance, achieving a lower final temperature and a higher temperature span after 60 min of operation. Moreover, the study highlights that cooling capacity and pumping work increase with higher nanoparticle concentrations, with a notable improvement of 64.95% in cooling capacity and 39.31% in pumping work for the 1.0% Al2O3 nanofluid compared to water. The Coefficient of Performance (COP) of the AMR system peaks at an optimal nanoparticle concentration of 0.2%, reaching 3.88, before declining due to increased pumping power requirements.

1D models of an active magnetic regeneration cycle for cryogenic applications

In investigation of an active magnetic regenerator (AMR) cycle operating at room temperatures, 1D models have been extensively used to accurately computing its performance metrics. However, extending these models to simulate an AMR cycle at cryogenic temperatures introduces inherent complexities and challenges. The broad temperature span and low operating temperatures required for cryogenic applications, such as hydrogen liquefaction, lead to significant density variations of the working fluid within the AMR that cannot be overlooked. In this work, two 1D AMR models assuming a compressible working fluid operating at cryogenic temperatures are demonstrated which address the large density variations and the numerical stiffness of the equations. The models exhibit good agreement with experimental and 2D numerical results of an AMR configuration designed for hydrogen liquefaction. A comparative study is conducted between the developed models and an incompressible AMR model at cryogenic temperatures shows that the incompressible model predicts cooling powers that are higher by a factor of up to 10 at high values of utilization, highlighting the error of assuming an incompressible fluid on estimating the performance metrics.

Synthesis, Characterization, and Magnetocaloric Properties of the Ternary Boride Fe2AlB2 for Caloric Applications.

The ternary transition metal boride Fe2AlB2 is a unique ferromagnetic "MAB" phase that demonstrates a sizable magnetocaloric effect near room temperature-a feature that renders this material suitable for magnetic heat pump devices (MHP), a promising alternative to conventional vapor compression technology. Here, we provide a comprehensive review of the material properties of Fe2AlB2 (magnetofunctional response, transport properties, and mechanical stability) and discuss alloy synthesis from the perspective of shaping these materials as porous active magnetic regenerators in MHPs. Salient aspects of the coupled magnetic and structural phase transitions are critically assessed to elucidate the fundamental origin of the functional response. The goal is to provide insight into strategies to tune the magnetofunctional response via elemental substitution and microstructure optimization. Finally, outstanding challenges that reduce the commercial viability of Fe2AlB2 are discussed, and opportunities for further developments in this field are identified.

Effect of gadolinium particle size on the performance of a magnetic refrigeration system

This study investigates the influence of gadolinium particle size on Magnetic Refrigeration (MR) system performance. Understanding how particle size of Magnetocaloric Materials (MCMs) within a fixed Active Magnetic Regenerator (AMR) volume affects cooling capacity and Coefficient of Performance (COP) is crucial for MR system design. However, research on this influence, especially using an experimental approach, has been surprisingly rare. This is despite the importance of considering various factors like total MCM mass, porosity, and pressure drop. The particles were categorized into five cases based on their sizes, which ranged from 0.50 to 2.00 mm opening sizes of the meshes. The magnetic field source produced the maximum 0.815 and 0.069 T for magnetization and demagnetization, respectively. A total four of AMRs were installed in the MR system for each case study. First, the porosity of the AMRs mostly increased as finer particles were filled up. This led to a tendency of lower mass of the MCMs in the same volume of the AMRs with smaller particles. Second, the temperature span showed the most outstanding value of 11.1 K in the 0.20 utilization factor using the finest particles (0.50–0.85 mm) in a no-load test. It also achieved a wider 8.3 K temperature span under 3.8 W of thermal load, outperforming the other sizes despite the least total mass of the MCMs. The major contribution to these results was the larger heat transfer area between the MCMs and heat transfer fluid inside the AMRs with the smaller particles. Nevertheless, the case with the second-finest particles (0.80–1.18 mm) exhibited the highest COP of 2.6, due to their favorable combination of moderately significant cooling capacity, reasonably small particle size, and elevated porosity that reduced pumping power demand and magnetic force.

A full solid-state conceptual magnetocaloric refrigerator based on hybrid regeneration

The environmental friendliness and high efficiency of magnetocaloric refrigeration make it a promising substitute for vapor compression refrigeration. However, the common use of heat transfer fluid in conventional passive magnetic regenerators (PMRs) and active magnetic regenerators (AMRs) makes only partial materials contribute to the regeneration process, which produces large regeneration loss and greatly limits the regeneration efficiency and refrigeration performance at high frequency. Herein, we propose a new conceptual hybrid magnetic regenerator (HMR) composed of multiple solid-state high thermal conductivity materials (HTCMs) and magnetocaloric materials (MCMs), in which both HTCM and MCM elements participate in the regeneration process. This novel working mode could greatly reduce regeneration losses caused by dead volume, pressure losses, and temperature nonuniformity in heat transfer substances to markedly improve regeneration efficiency at high working frequencies. Using the experimentally obtained adiabatic temperature change and magnetic work and with the help of finite element simulation, a maximum temperature of 26 K, a dramatically large cooling power of 8.3kW/kg, and a maximum ideal exergy efficiency of 54.2% are achieved at the working frequency of 10Hz for an ideal prototype device of a rotary HMR magnetocaloric refrigerator, which shows potential for achieving an integrative, advanced performance against current AMR/PMR systems.

Improving the performance of room temperature rotary magnetic refrigerators via magnet shape optimization

A magnetic structure intended for use in a room-temperature rotary active magnetic regenerator (AMR) is presented, under construction at the University of Genoa. Given the overall size of the regenerator and the thickness of the gap, the magnet design is optimized to produce the highest possible magnetic field difference between two adjacent regions. Magnet shape optimization is obtained by introducing a geometry with four degrees of freedom corresponding to the position of the edges of each magnet, plus the remanence angle. This approach serves two main purposes: the primary is to increase the magnetic induction and, to follow, some effort is made to minimize the volume and weight of the expensive NdFeB magnets, while preserving the cooling performance. So, a balance between these two goals must be achieved. After a rough preliminary sizing, a parametric investigation is performed toward these targets and some shapes are presented. The magnetic flux density in the gap, and other consolidated and novel performance indices, are evaluated and compared to those found in the literature for similar devices. The final design achieves, in the air gap, a maximum induction value of 1.045 T, and an average flux density of 0.83 T in a volume per unit length of 0.00268 m3/m in the high induction region. This is accomplished by using 0.00606 m3/m of magnetic material (N50, NdFeB). The magnet designs presented here exhibit a well-balanced performance (in terms of greater cooling for the same magnet weight) compared to earlier designs for similar AMR devices.

Development and experimental analysis of a multi-bed active magnetic regenerator

Room temperature magnetic refrigeration technology is a potentially efficient and environmentally friendly refrigeration technology. A magnetic refrigeration prototype with two high/low magnetic field regions was designed and built. The device consists of eight beds, using gadolinium particles as the magnetocaloric material, with a total filling mass of 1.35 kg. The hydraulic system consists mainly of a magnetic centrifugal pump, solenoid valves, and check valves. The flow of the heat transfer fluid through the regenerators is controlled by controlling the opening and closing of the solenoid valves. The no-load temperature span, cooling capacity, power consumption, and COP of the regenerators were investigated separately. The maximum no-load temperature span of 17.5 K was obtained at an AMR frequency of 0.5 Hz and flow rate of 1.15 L/min. The total power consumption and the magnetic power and pumping power were analyzed for different operating conditions.

Gadolinium: A DFT exploration of structural, electronic, and magnetic features in bulk and film configurations for enhanced magnetocaloric understanding

Gadolinium stands as the favored choice among magnetic refrigerant materials for numerous active magnetic regenerator (AMR) prototypes due to its remarkable ability to exhibit a substantial change in magnetic entropy. This unique characteristic arises from its status as one of the elemental ferromagnets with a high Curie temperature, closely aligning with room temperature conditions, and undergoing a second-order magnetic phase transition. In this comprehensive study, we employ density functional theory (DFT) calculations to explore the structural, electronic, and magnetic properties of both Gadolinium bulk and film configurations. Our primary objective is to gain a deeper understanding of the intricate physics underlying the intriguing magnetocaloric features observed in Gadolinium. This investigation provides valuable insights into the potential applications and the broader implications of Gadolinium in the realm of magnetic refrigeration technology.

Compatibility of LaFe13−x−yMnxSiyH1.6 and Eutectic Liquid GaInSn Alloy

The heat transfer rate of magnetocaloric regenerators is a topic of extensive research and the cyclability of these regenerators is critical to the operation of systems with a high coefficient of performance (e.g., potentially >22, significantly higher than typical vapor compression cooling technologies). To enable a high operating frequency that will result in a high specific cooling power, the heat transfer fluid should have high thermal conductivity and lower specific heat, i.e., higher thermal diffusivity. Eutectic metal alloys possess these qualities, such as gallium–indium–tin (Galinstan), whose thermal diffusivity has been found to be approximately an order of magnitude higher than water. For this study, the effects of eutectic liquid Galinstan exposure on the phase stability of LaFe13−x−yMnxSiyH1.6 magnetocaloric powders in an active magnetic regenerator device were investigated. The powders were characterized before and after exposure to Galinstan using X-ray diffraction, in which the phases were determined using the Rietveld refinement technique and X-ray fluorescence. It was found that after Galinstan exposure, hydrogen containing phases were present in the powder, suggesting that the hydrogen was lost from the magnetocaloric phase. The magnetocaloric phase degradation indicates that the powder was incompatible with the Galinstan metal in an environment with moisture.

Long-time aging of La(Fe,Si,Mn)13Hz microparticles using different fluids for magnetic refrigeration systems

La(Fe,Si,Mn)13Hz alloys are promising solid-state refrigerant candidates for room-temperature magnetocaloric refrigeration due to their giant magnetocaloric effect, adjustable Curie temperature (TC) and low rare-earth content. For enhanced efficiency, the magnetocaloric material (MCM) is configured into an active magnetic regenerator (AMR), a porous, layered component with a chemically-tuned TC gradient. The porous structure facilitates heat exchange with a working fluid. It is crucial to preserve the thermomagnetic properties, such as TC and the magnetocaloric effect intensity, during refrigeration cycles. This study conducts a systematic investigation of the stability of three batches of La(Fe,Si,Mn)13Hz magnetocaloric microparticles, each with different values of TC. The commercially available microparticles (average size about 620 µm), which simulate AMR applications, underwent a 1-year immersion in deionized water and three water mixtures with corrosion inhibitors: Entek FNE (2 % vol.), ME-1 (5 %. vol.) and ME-3 (5 % vol.). Optical and scanning electron microscopy revealed surface changes within the first week of immersion in water and later in two fluids. The TC shifted towards higher temperatures (up to 13 K) after immersion, especially in water and in the ME-3-containing medium. After 40 weeks, the Entek FNE mixture caused some damage to the magnetocaloric materials. The lattice parameter of the La(Fe,Si,Mn)13Hz magnetocaloric phase changed, and magnetic entropy decreased for most aqueous media. Only ME-1 proved effective in preserving magnetocaloric microparticle properties for all TCs over a year, making it a potential candidate for long-term prototypes and commercial products.

Моделирование системы магнитного охлаждения и синтез регулятора ее холодопроизводительности

The article reviews existing designs of cooling systems and analyzes problems in their development and operation. As a result, a magnetocaloric refrigerator is selected as a research object. The refrigerator device under study and the processes occurring therein are investigated to develop a mathematical apparatus for simulating an active magnetic regenerator as the most problematic part of the refrigerator device. Subsequently, the system for controlling cooling capacity is synthesized and implemented in software form to regulate temperature fluctuations in steady-state mode at the boundary with heat dissipation. Simulation of transient heat transfer processes between a magnetic material and a coolant is carried out taking into account the spatial distribution of the object under consideration. The setting of the regulator is based on the static characteristic of changes in the coolant temperature on the value of magnetic induction in the orthocenter of the boundary plane with the cold heat exchanger.

Static and dynamic modeling and identification of a magnetic refrigerator

In this paper, an experimental study of a magnetic refrigerator was carried out to identify static and dynamic models, which can be used for proposing and tuning control strategies. For the experimental evaluation, a 40liter thermally insulated compartment was coupled to a magnetic refrigeration system equipped with an active magnetic regenerator. The influence of fluid flow rate, blow fraction, and magnetic cycle frequency on the temperature behavior inside the refrigerated compartment and on the power consumption of the system was evaluated. The results of the characterizations show that it is possible to reach equivalent cabinet temperatures by changing the flow rate of the thermal fluid or the cycle frequency. However, the former has a greater influence on the temperature of the cabinet, and the latter has a greater impact on the energy consumption and is associated with slower transients. Additionally, the temperature of the cabinet at steady state showed a parabolic behavior with respect to the fluid flow rate, demonstrating that there is an optimal flow rate for a given operating condition.

The feasibility of using magnetic refrigeration cycles in the thermal management of rechargeable batteries in electric cars

This is the first study that intends to check the feasibility of using a magnetic refrigerator (MR) in the thermal management of rechargeable batteries instead of other conventional passive/active cooling techniques. A mathematical model has been generated to study the cooling performance of the proposed system at different conditions, including synchronized and asynchronized cooling at different discharge rates and ambient temperatures, in addition to exploring the effect of using water-based copper (Cu) nanofluid as a heat transfer fluid in a spherical packed bed active magnetic regenerator on the cooling performance. The proposed system can maintain the maximum temperature of the battery pack to less than 35 °C with high coefficients of performance (COPs) [between 4.8 and 9.7] during synchronized and asynchronized cooling at an ambient temperature of 25 °C and different discharge rates. The system can operate with COP higher than 1 at an ambient temperature up to 40 °C during 0.5 discharge rate, and up to 38 °C ambient temperature during 1 discharge rate. The MR can work with COP of 5.3 compared to 3.82 for vapor compression refrigeration system (VCRS) if the two systems meet a 3-kW cooling load. The study reveals that MR outperforms many active cooling techniques especially when appropriately integrated with the thermal management of the vehicle cabin.

Widening of working temperature range in Mn5-xCuxGe3 (x = 0.1 and 0.3) magnetocaloric compounds by compositional tuning

This study presents the effect of Cu doping on the fundamental properties, magnetocaloric effect, and critical behavior of Mn5Ge3 system. Mn5-xCuxGe3 compounds with x = 0.1 and 0.3 conform D88-hexagonal structure. The unit cell volume decreases, and MnI-MnI distance increases with Cu content. This modifies the exchange interaction and impacts Curie temperature and saturation magnetization accordingly. The critical exponents β and γ of x = 0.1 compound are of 3D Ising class, while the x = 0.3 compound shows non-conventional behavior with its γ lying within the 3D Ising framework and β lying between 3D XY and Heisenberg classes. Both the compounds have extended-type spin interactions, and the decay of the exchange integrals has been calculated. Mn5-xCuxGe3 compounds clearly outperform most materials of Mn5Ge3 class in terms of the magnetocaloric effect. They show an appreciable reversible isothermal entropy change across a wide temperature span with a large relative cooling power near the room temperature effect. These compounds can be combined with other suitable Mn5Ge3 materials and used in ‘active magnetic regenerative (AMR)’ systems as layered refrigerants for more efficient magnetocaloric cooling.

Power output of magnetocaloric materials during heat and cold decoupling by unidirectional fluid flow

This article presents the results of a novel concept of heat and cold decoupling from magnetocaloric materials (MCM) by unidirectional fluid flow. An experimental setup was developed to analyse the heat/cold decoupling and determine the optimal process parameters. Three different kinds of magnetocaloric material samples were analysed by using this setup. Comparing the measuring results to those of existing active magnetic regenerator (AMR) systems shows a very good performance and indicates a higher achievable thermal power output when using a unidirectional fluid flow.

Numerical simulation of a multistage magnetic refrigeration system in the temperature range of liquid hydrogen

Magnetic refrigeration is an important new refrigeration technology in the temperature range of liquid hydrogen. A multistage magnetic refrigeration system between 20 K and 80 K has been proposed, which includes three-stage active magnetic regenerators (AMRs). Based on the multistage system, a two-dimensional transient AMR model is established to research the cycle performance mechanism by considering the compressibility of helium, which has not been done before. Firstly, to simplify the simulation difficulty, the AMR model with ideal magnetocaloric materials (the constant isothermal entropy change of 5.4 J/(kg·K) at 1 T) are investigated in the temperature range between 60 K and 80 K. Some parameters including particle diameter, fluid flow fraction, and filling mass of magnetocaloric materials have been compared and analyzed. Based on the above simulation results, the AMR model with real magnetocaloric materials has been done. In the three-layer AMR, the maximum cooling power of 71.04 W at the cooling temperature of 60 K has been obtained, which is 80.17% larger than that of the one-layer AMR. Then, the cooling performance of the multistage magnetic refrigeration system has been studied. In the system, six magnetocaloric materials are filled in three-stage AMRs based on the filling method of adiabatic temperature change. With the optimal mass flow rates of each stage AMR, the maximum cooling power of 40.09 W has been obtained in the multistage system, and the corresponding thermodynamic second efficiency has been 28.14%.